The present invention relates to display backlights which make it possible to display any message in the visible light range, and more especially, but not exclusively, display backlights for use in advertising or similar.
Numerous realisations of display panels of the illuminated type are known. However, these realisations are not sufficiently simple to permit the manufacture in large quantities of advertising display panels.
The aim of the present invention is also to realise a display backlight, the structure of which overcomes the above-mentioned disadvantages of display backlights of prior art.
More precisely, the subject matter of the present invention is a display backlight capable of being disposed in an environment having an optical index with a value n1 characterised in that it comprises:
a plate formed from a first material transparent for at least one light wavelength in the bandwidth of visible light, said first material having an optical index with a value n2 higher than the value n1, said plate being delimited by two substantially parallel plane surfaces having a substantially optical polish and by a peripheral edge,
a source of visible light,
means for coupling said source of visible light with the peripheral edge of said plate such that the rays emitted by said source of visible light penetrate into the plate via this peripheral edge and are propagated inside the plate between the two plane surfaces mainly by total reflections, and
at least one first layer formed from a second material transparent for said wavelength, said first layer being disposed in optical contact with a first of the two plane surfaces of the plate, said second material having an optical index with a value n3 higher than the value n1.